1. Field of the Invention
The invention relates to a cooling system and a vehicle that includes the cooling system and, more particularly, to a cooling system that cools a heat generating source by utilizing a vapor compression refrigeration cycle and a vehicle that includes the cooling system.
2. Description of Related Art
In recent years, hybrid vehicles, fuel cell vehicles, electric vehicles, and the like, that run with driving force of a motor become a focus of attention as one of measures against environmental issues. In such vehicles, electrical devices, such as a motor, a generator, an inverter, a converter and a battery, exchange electric power to generate heat. Therefore, these electrical devices need to be cooled.
Japanese Patent Application Publication No. 2000-73763 (JP 2000-73763 A) describes a cooling system for a hybrid vehicle. The cooling system includes a first cooling circuit, a second cooling circuit and a third cooling circuit. The first cooling circuit selectively or simultaneously cools a power control unit that executes drive control over a drive motor, an engine cylinder head and the drive motor. The second cooling circuit cools an engine cylinder block. The third cooling circuit cools the power control unit. The cooling system switches a circulation path of coolant among the cooling circuits on the basis of the operating states of an engine, motor and air conditioner. Other than JP 2000-73763 A, a technique relating to a cooling device or cooling system is described in Japanese Patent Application Publication No. 2005-90862 (JP 2005-90862 A), Japanese Patent Application Publication No. 2007-69733 (JP 2007-69733 A), Japanese Patent Application Publication No. 2009-229014 (JP 2009-229014 A), Japanese Patent Application Publication No. 2005-271906 (JP 2005-271906 A), and the like.
In the above-described cooling system, an engine cooling system and a hybrid cooling system that cools the power control unit, and the like, are provided, and flow passages between these cooling systems are switched by control valves. Therefore, the configuration of the cooling system becomes complex, so cost increases.
In contrast to this, it is conceivable to cool hybrid electrical devices by utilizing an air conditioner cooling system. By so doing, it is possible to reduce cost by simplifying the hybrid cooling system. Furthermore, in this case, when the air conditioner is stopped, it is conceivable that the hybrid electrical devices are cooled without operating a compressor by forming a heat-pipe cooling circuit and, by so doing, power consumption is reduced.
However, in the heat-pipe cooling circuit, a phenomenon called dryout that all the refrigerant dries out may occur if the amount of refrigerant in a heat-pipe cycle is short with respect to the amount of heat radiation that is required to protect a heat generating source, such as the hybrid electrical devices. When dryout occurs, the performance of cooling the heat generating source decreases, so the temperature of the heat generating source problematically increases. In terms of this point, no measures are taken into consideration for the above-described cooling system for a hybrid vehicle.